I'm not sure from where you are needing to access the path (ArcMap, ArcCatalog, etc) but here are a couple of examples:
 
'ArcMap
Dim pMxDoc As IMxDocument
    Dim pFL As IFeatureLayer
    Dim pDS As IDataset
    Dim pWS As IWorkspace
    Set pMxDoc = ThisDocument
    Set pFL = pMxDoc.SelectedLayer
    Set pDS = pFL.FeatureClass
    Set pWS = pDS.Workspace
    MsgBox pWS.PathName & "\" & pDS.Name
 
'ArcCatalog
Dim pGxApp As IGxApplication
    Dim pGxObj As IGxObject
    Dim pGxArray As IGxObjectArray
    Set pGxApp = Application
    Set pGxObj = pGxApp.SelectedObject
    Set pGxArray = New GxObjectArray
    pGxArray.Insert -1, pGxObj
    MsgBox pGxArray.Item(0).FullName